Wireless point multipoint system

ABSTRACT

A patch array antenna includes a planar base on which is defined a ground plane and feed positions that are electrically isolated from the ground plane. A plurality of patch elements are configured to resonate over a predetermined frequency range. Each patch element is isolated from the ground plane and disposed on the base over the ground plane so that an air dielectric is defined between the patch element and the ground plane. Each patch element defines a resonant portion that is electrically connected to a respective feed position. A feed network is defined on the base that electrically connects the feed positions to one or more output points on the base.

This is a division of U.S. application Ser. No. 10/264,983, filed Oct.4, 2002, which is a continuation-in-part of U.S. application Ser. No.10/263,210, filed Oct. 1, 2002, now abandoned, entitled “Wireless Pointto Multipoint System,” the entire disclosures of which are incorporatedby reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to wireless point to multipoint systems.Systems are known in which a base station transmits electromagneticsignals to, and receives electromagnetic signals from, subscriber unitswithin a sector allocated to the base station. User devices are attachedto each subscriber unit, and the base station forwards data to the userdevices through their corresponding subscriber units as the data isreceived by the base station from an outside source, for example theInternet. In one type of known system, the base station designatescertain time periods, called “contention periods,” in which thesubscriber units are eligible to transmit back to the base station. If asubscriber unit has data to be forwarded to the base station, thesubscriber unit does so during the contention period.

Wireless systems are also known which do not have contentions periodsbut which divide up the available time into slots during which eachsubscriber unit is allowed to transmit back to the base station. Thenumber of slots is directly related to the number of subscribers in thesector. These type systems also tend to incorporate base stations whichwill reserve a portion the available bandwidth for traffic from thesubscriber to the base station and a percentage of available bandwidthfor traffic from the base station to the subscriber.

Wireless systems are known that include a plurality of user devicesconnected to a subscriber unit that wirelessly communicates with a basestation. When the base station receives an Ethernet packet destined toone of the user devices, the base station refers to a database tablethat associates each user device with its subscriber unit. The tableincludes a predetermined limit of user devices, for example eight, thatmay be associated with a subscriber unit in the table at any time. Insearching for a user device address in the table, such systems searchsequentially through the table addresses for the desired address.Accordingly, such tables are limited in the number of user devices thatcan be associated with any given subscriber unit and become inefficientin use of the table as the number of entries increases. To reduce thenumbers of entries, multiple subscriber units may be attached to aswitch, the address of which is then provided in the table.

SUMMARY OF THE INVENTION

The present invention recognizes and addresses disadvantages of priorart constructions and methods. Accordingly, it is an object of thepresent invention to provide an improved wireless point to multipointsystem.

This and other objects are achieved by a point to multipoint wirelesscommunication system having an access point configured to receive datasignals from an external system. The access point has an antenna, aprocessor, and circuitry in communication with the access point antennaand controlled by the access point processor to transmit wirelesselectromagnetic signals corresponding to the data signals to, and toreceive wireless electromagnetic signals from, a geographic area. Aplurality of subscriber units are disposed within the area, eachsubscriber unit having an antenna, a processor, and circuitry controlledby the subscriber unit processor to transmit wireless electromagneticsignals to, and receive wireless electromagnetic signals from, theaccess point for communication with the external system. The accesspoint allocates data bandwidth among the subscriber units based at leastin part on the past use of bandwidth to transmit data between the accesspoint and the subscriber units.

A method according to an embodiment of the present invention forallocating bandwidth availability within a point to multipoint wirelesscommunication system includes providing an access point. The accesspoint has an antenna, a processor and circuitry in communication withthe access point antenna and controlled by the access point processor totransmit wireless electromagnetic signals to, and receive wirelesselectromagnetic signals from, a geographic area. A plurality ofsubscriber units are provided within the area, each subscriber unithaving an antenna, a processor and circuitry controlled by thesubscriber unit processor to transmit wireless electromagnetic signalsto, and receive wireless electromagnetic signals from, the access point.Data bandwidth is allocated among the subscriber units based at least inpart on the past use of bandwidth to transmit data between the accesspoint and the subscriber units.

A patch array antenna according to an embodiment of the presentinvention includes a planar base on which is defined a ground plane andfeed positions that are physically isolated from the ground plane. Aplurality of patch elements are configured to resonate over apredetermined frequency range. Each patch element is isolated from theground plane and is disposed on the base over the ground plane so thatan air dielectric is defined between the patch element and the groundplane. Each patch element defines a resonant portion that iselectrically connected to a respective feed position. A feed network isdefined on the base and electrically connects the feed positions to oneor more output points on the base.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended drawings, in which:

FIG. 1 is a block diagram illustrating a wireless point to multipointsystem in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram of a cell as shown in FIG. 1;

FIG. 3 is a functional block diagram illustration of the wireless pointto multipoint system as shown in FIG. 1;

FIG. 4 is a functional block diagram illustration of an access pointtransmitter and receiver for use in accordance with an embodiment of thepresent invention;

FIG. 5 is a circuit block diagram of the transmitter and receiver asshown in FIG. 4;

FIG. 6 is a diagrammatic illustration of an address table entry used inaccordance with an embodiment of the present invention;

FIG. 7A is a flow diagram of a packet processing procedure in accordancewith an embodiment of the present invention;

FIG. 7B is a flow diagram of a packet processing procedure in accordancewith an embodiment of the present invention;

FIG. 8 is a functional block diagram illustration of a subscriber unittransmitter and receiver in accordance with an embodiment of the presentinvention;

FIG. 9 is a group flow diagram illustration within a polling algorithmaccording to an embodiment of the present invention;

FIG. 10 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 11 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 12 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 13 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 14 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 15 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 16 is a flow diagram of part of a polling algorithm in accordancewith an embodiment of the present invention;

FIG. 17 is a flow diagram illustrating an information rate managementprocedure in accordance with an embodiment of the present invention;

FIGS. 18A and 18B are a diagrammatic illustration of command and datapackets transmitted from the access point in an embodiment of thepresent invention;

FIGS. 19A and 19B are a diagrammatic illustration of command and datapackets transmitted from subscriber units in accordance with anembodiment of the present invention;

FIG. 20 is a perspective view an antenna array in accordance with anembodiment of the present invention;

FIG. 21 is a rear plan view of the antenna array illustrated in FIG. 21;

FIG. 22 is a back plan view of an antenna array in accordance with anembodiment of the present invention;

FIG. 23 is a partial top view of an antenna array in accordance with anembodiment of the present invention;

FIG. 24 is a top view of a main board of the antenna as in FIG. 23;

FIG. 25 is a bottom view of a secondary board of the antenna as in FIG.23; and

FIG. 26 is a partial top view of an antenna array in accordance with anembodiment of the present invention.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to presently preferred embodimentsof the invention, one or more examples of which are illustrated in theaccompanying drawings. Each example is provided by way of explanation ofthe invention, not limitation of the invention. In fact, it will beapparent to those skilled in the art that modifications and variationscan be made in the present invention without departing from the scope orspirit thereof. For instance, features illustrated or described as partof one embodiment may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

A. System Configuration

An exemplary deployment of a point to multipoint fixed wireless networksystem 10 comprised of three base station cells is shown in FIG. 1. Eachbase station cell 12, 14 and 16 is divided into sixty degree (60°)coverage areas, referred to herein as “sectors,” in which are disposedsubscribers wishing to access the Internet or other external systems. Abase station having six access points 18 is located at the center of thesix sectors 20, as shown in FIG. 2.

The cells shown in FIG. 1 represent geographic areas. At the center ofeach cell, and therefore at the convergence of the six sectors, is atower or other suitable structure on which an access point for eachsector is mounted facing out into its sector, as shown in FIG. 2. Thatis, the collection of access points comprises the base station. Asdescribed in more detail below, each access point includes an antennathrough which the access point transmits electromagnetic signals to, andreceives electromagnetic signals from, one or more subscriber units 22(FIG. 2). Each subscriber unit also contains an antenna and circuitrythrough which the subscriber unit receives data transmissions from theaccess point destined for user devices attached to the subscriber unit.A subscriber unit also transmits data from its user device(s) to theaccess point.

To avoid interference among sectors, each access point uses an antennapolarization and transmission frequency different from its adjacentaccess points. In the example shown in FIG. 2, adjacent sectorsalternate between vertical and horizontal polarization.

Furthermore, each access point operates at a specific frequency channel.As should be understood, the FCC regulates and allocates frequencybandwidths used in communication systems. The embodiment of the presentinvention described herein, for example, operates over a total frequencyrange from 5.725 GHz to 5.850 GHz. This frequency range is divided intofrequency channels within which the individual sectors operate. Theaccess point and subscriber units in each sector modulate data on theirsector's carrier frequency, which is centered in the channel, usingcomplementary code keying, a form of quadrature phase shift keying withhighly uncorrelated phase shift patterns. Complimentary code keying,which is also typically used by wireless LAN systems, should be wellunderstood in this art and is, therefore, not discussed in detailherein. Furthermore, it should be understood that other suitablemodulation techniques may be employed and that complimentary code keyingis provided for purposes of example only.

The 5.725 GHz-5.850 GHz frequency band is divided into six channels,leading to the division of each cell into its six sectors, eachoperating on one of the six channels. The number of available channelsmay be increased by using each channel frequency twice in a cell withinsectors having opposite polarity. Assume, for example, that oppositelyfacing access points AP1 and AP4 in FIG. 2, along with their respectivesubscriber units, operate on the same frequency but with differentpolarization. In such an arrangement, each cell uses each of threechannels twice. Since six channels are available, each cell tower mayhost two rings of six access points, one ring above the other, whereeach ring uses a different set of three frequency channels. Thedifference in polarization and physical orientation between AP1 and AP4reduces the risk of interference between the two access points, but theaccess points may preferably be shielded from one another to providefurther protection.

Any suitable shielding may be used between access points or between tworings of access points. Shielding may be provided between the rings toprevent interference. For example, each access point may be received ina concave shield that opens into the access point's sector. The shieldis constructed from an underlying metal sheet coated with a radiofrequency absorbing material. Such shields are commonly used and arethereby not described in more detail herein.

Returning to FIG. 1, base stations are disposed proximate each other toestablish adjacent cells 12, 14 and 16. Each base station communicateswith an Internet service provider point of presence 24 through a wiredor wireless backhaul 26. The ISP point of presence includes a router andtelco interface 28 that communicates with the Internet 30 through atelecommunications connection 32.

FIG. 3 provides a block diagram illustration of a single sector coveringthree subscribers, each connected to a data interface device. Often, thedata interface device will be a switch, computer or other Ethernetdevice 34, but it may be any other suitable device that receives dataand collects the data into a predetermined form for output to acommunication system. Ethernet-based cameras, for example, may be usedin security systems to output video images for transmission to remotelocations. More commonly, however, devices 34 are computers havingEthernet cards that communicate over Ethernet cables 36 to a subscribertransmitter/receiver unit 22. Ethernet connections are in highly commonuse and, for ease of explanation, the present discussion presents thesystem in terms of an Ethernet example.

Each subscriber unit includes a pair of antenna arrays 38 and 40 forwireless communication with an access point receiver/transmitter 18.Antenna arrays 38 and 40, which are described in more detail below, areof opposite (for example horizontal and vertical) polarization, so thatthe subscriber unit may communicate in either polarization. Similarly,access point 18 defines horizontal and vertical polarization antennaarrays 42 and 44.

Each base station in each cell (FIG. 1) includes an Ethernet switch 46that communicates with each access point 18 at the base station.Ethernet switch 46 communicates with the point of presence router 28over backhaul 26. Router 28, in turn, communicates with the Internet 30over telecommunications interface 32.

The construction and operation of Ethernet switches should also beunderstood in this art. As should also be understood, such switches maybe used to facilitate communications not only from the access point topoint of presence router 28, but also communications from one accesspoint to another within the same cell. Thus, the system may be used tofacilitate communications among subscribers in different cells throughan interconnection of Ethernet switches. Moreover, the system may beused in a local network without connection to the Internet. For example,the local network may comprise a single cell with multiple access pointscommunicating with a single Ethernet switch controlled by a servercomputer. Subscriber transmissions intended for a subscriber in adifferent sector are passed by the access point to the Ethernet switch,which forwards the transmission to the access point in the appropriatesector. The system may also be arranged so that subscribers within thesame sector may communicate with each other through an access pointwithout communication with the switch. All such communications may beeffected using TCP/IP protocol, which should be well understood in thisart.

FIG. 4 provides a functional block diagram illustration of an accesspoint transmitter/receiver 18 as it receives Ethernet packets andtransmits corresponding radio frequency (RF) packets to the subscriberunits (downstream communications) and as it receives RF packets from thesubscriber units and outputs corresponding Ethernet packets to anupstream Ethernet system (upstream communications). FIG. 4 is describedin conjunction with FIG. 5, which provides a circuit block diagram ofthe access point.

The access point receives Ethernet packets at 47 through an Ethernetport 48 from an Ethernet connection to Ethernet switch 46 (FIG. 3).Ethernet port 48 is a physical interface, for example a cableconnection, as should be understood in this art.

As should also be understood, an Ethernet packet is a sequence of bitscomprised of a preamble, a header, a payload and a checksum. Thepreamble includes timing signals to enable a receiver's microprocessorto set up an internal clock so that the receiver properly receives thepacket. The header includes a delimiter (a fixed pattern of bits thatidentifies the packet as an Ethernet packet), a destination address, asource address and a length field. The payload is the data conveyed bythe packet. Ethernet packets generally range from 64 bytes to 1,514bytes in length. To support virtual LAN tagging, the present systemsupports up to 1600 byte packets. Ethernet packet structure is definedin IEEE Standard 802.3 and should be well understood in this art.Moreover, the content and size of the Ethernet packets is determined bya higher-order protocol (for example, TCP/IP) at a system upstream fromthe access point. The higher-order protocol is not critical to thepresent system and is not described further herein. In the presentlydescribed embodiment, the access point need only recognize the packetand determine the packet's destination.

An Ethernet packet transceiver 50 receives packets from Ethernet port 48and transfers the packets to a buffer memory 52 over a local bus 54.Transceiver 50 is comprised of a physical layer (PHY) component 56 and amedia access control (MAC) component 58. In one embodiment, thesecomponents are integrated circuits (LAN83C180 and LAN91C110,respectively), available from Standard Microsystems Corporation ofHauppauge, N.Y.

A microprocessor 60 polls transceiver 50 at a rate sufficient to emptybuffer 52 faster than the system's maximum data rate, in this example 10Mbits per second. Upon polling the transceiver, the microprocessortransfers any packets in buffer 52 to a system DRAM 62 over system bus64. The microprocessor then reads the destination address from thepacket header to determine to which user device the packet shouldultimately be directed. The access point and subscriber unitmicroprocessors are programmed in C to perform the functions describedherein, although it should be understood that any suitable programminglanguage could be used.

The access point communicates with user devices in its sector viasubscriber units. Thus, the access point maintains in a MAC-SU listmanager 69 (stored at SDRAM 62) a dynamic table that associates userdevices to the respective subscriber units to which they are attached. Asingle subscriber unit may have multiple computers or other devicesattached to it, for example as part of a local network that communicatesthrough the subscriber unit with the Internet or other networks ordevices. Thus, and referring also to FIG. 6, the MAC-SU List hasmultiple entries 102, each of which lists a subscriber unit in theaccess point's sector (by its subscriber identification number, or SUID,104) and a MAC address 106 of a user device associated with thesubscriber unit. The entry also includes a time stamp 108 correspondingto the time at which the entry was created or updated.

The MAC-SU List is dynamic in that the access point modifies the table'sinformation based on communications managed by the access point. In thepresently described embodiment, the access point creates and modifiesthe table as it receives incoming packets from the local Ethernet portat 47 or the RF transmitter/receiver at 90. For example, assume that anew system is installed with subscriber units and with user devicesattached to the subscriber units. Prior to the access point's receipt ofany packets for the user devices, the MAC-SU List is empty. It has noentries associating user devices with subscriber units.

Thus, upon receiving the first packet and reading its destination MACaddress, the access point microprocessor does not find the packet'sdestination address in the MAC-SU List and therefore does not know towhich subscriber unit to transmit the packet. The access point thusbroadcasts the packet to all subscriber units in its sector, which inturn receive the packet and provide it to their user devices. If thetarget user device is present in the sector and receives the packet, itresponds to its subscriber unit, which then forwards the response to theaccess point.

The subscriber unit sends an Ethernet packet that includes the userdevice's MAC address appended with the subscriber unit's SUID. Inresponse, and referring again to FIGS. 4 and 5, microprocessor 60creates at 69 an entry in the MAC-SU List that includes the subscriberunit's SUID 104, the user device's six byte MAC address 106, and timestamp 108 of the time at which the entry was made. If the access pointthereafter receives a packet with the same destination address, themicroprocessor reads the MAC-SU List entry, identifies the subscriberunit associated with the destination address, and transmits the packetonly to the identified subscriber unit. It should be understood thatwhile the presently described embodiment utilizes an SUID number 104 toidentify subscriber units in the MAC-SU List, any suitableidentification could be used. The access point continues to build theMAC-SU List as it receives packets destined for other user devices.

In the presently described embodiment, the MAC-SU List holds up to 2,000entries. The microprocessor searches these entries using a blanketsearch algorithm based on the Ethernet packet's destination address. Thesearch algorithm uses the last byte in the address as an index in whichto group the search. That is, the microprocessor reads the destinationaddress and moves to those entries in the MAC-SU List whose user deviceMAC addresses have the same last byte. The search is then conductedwithin this index group, as opposed to the entire 2,000-entry table.Within the index group, the microprocessor subsequently reads each userdevice address until finding the address identified in the Ethernetpacket. If the microprocessor finds the desired address, the accesspoint selects the corresponding subscriber unit address in the entry andupdates the time stamp.

If the microprocessor does not locate the desired address, the accesspoint designates the packet as requiring broadcast to all subscriberunits in the sector, as described above, and creates a new MAC-SU Listentry upon receiving a response from the subscriber unit to which thetarget user device is attached. Thus, the MAC-SU List grows with thenumber of user devices. When the MAC-SU List is full, and themicroprocessor needs to install an additional entry, the microprocessorscans the index group to which the new entry applies, finds and deletesthe oldest entry (i.e. the entry with the earliest time stamp) in thegroup, and enters the new entry. Furthermore, when searching any indexgroup for a subscriber unit, the microprocessor reads the time stamp ofeach entry and deletes any entry older than a predetermined period, forexample five minutes. In this manner, the system constantly updates theMAC-SU List to include those user devices that are currently active.Particularly where the number of entries in the MAC-SU List is greaterthan or equal to the number of user devices typically active at anygiven time in the access point's sector, the MAC-SU List facilitatescommunication with the subscriber units so that the access point mayeffectively support a much greater number of user devices. Thus, itshould be understood that the MAC-SU List may be structured as desiredto have a number of entries suitable for a given system. Furthermore, itshould also be understood that various search algorithms may be employedin order to locate destination addresses within the MAC-SU List.

FIG. 7A illustrates the steps executed by the microprocessor uponreceiving a downstream Ethernet packet at 110. The microprocessor firstchecks at 112 to determine whether the packet is a unicast, broadcast,or multicast packet. Broadcast and multicast packets are describedbelow. Generally, however, these are packets intended for broadcast toall subscriber units, and their destination address field therefore hasa special MAC address. If the incoming Ethernet packet's destinationfield is for broadcast or multicast at 112, the microprocessordetermines that there will be no single corresponding subscriber unit inthe MAC-SU List and exits the search routine at 114.

If a packet has a MAC address for a user device, the microprocessorreads the last byte of the packet's destination address at 116 and movesat 118 to those entries in the MAC-SU List whose user device MACaddresses 106 have the same last byte. Moving to the first address inthis group at 120, the microprocessor compares the destination addresswith the table MAC address. If they match, the microprocessor updatesthe time stamp 108 for this entry at 122 and returns the subscriber unitSUID 104 at 124. The microprocessor then knows to which subscriber unitto address the RF data packet as described above.

If the first entry does not have a matching user device MAC address at120, the microprocessor then checks the entry's time stamp at 126 todetermine whether it is older than five minutes. If so, the entry isdeleted from the MAC-SU List at 128, and the microprocessor returns tothe next entry in the index group at 118. If the time stamp has notexpired at 126, the microprocessor moves directly to the next entry inthe index group at 118.

This cycle repeats throughout the index group entries until a match isfound or until the microprocessor reviews all index group entrieswithout finding a match. If no match is found, the microprocessor exitsthe search at 130 and broadcasts the packet to all subscriber units, asdiscussed above.

FIG. 7B illustrates the steps executed by the microprocessor uponreceiving an upstream packet at 110. At 116, the microprocessor locatesthe last byte of the user device MAC address in the packet and moves at118 to those entries in the MAC-SU List whose user device MAC addresseshave the same last byte. The microprocessor executes the search steps120-128 in the same manner as for downstream packets. After updating thetime stamp at 122, the microprocessor proceeds with packet processing at124. If no match is found in the index group, however, themicroprocessor creates a new entry at 130, saves the entry at 132 andproceeds with packet processing at 124.

Returning to FIGS. 4 and 5, when the microprocessor locates thesubscriber unit associated in the MAC-SU List with the Ethernet packet'sdestination address, the microprocessor checks SU database 67 todetermine if the subscriber unit is valid. A valid subscriber unit isone whose SUID is stored in the SU database and which the access pointhas successfully authenticated, as discussed below.

The microprocessor checks at 71 whether the subscriber unit has exceededits available information rate. In the presently described embodiment,each subscriber unit is assigned a committed information rate (CIR) anda maximum information (MIR). The CIR is the minimum information rate thesystem is committed to provide the subscriber unit. That is, thesubscriber unit will always be allocated this rate or higher. The MIR isthe maximum information rate available to the subscriber unit. If thesubscriber exceeds its MIR, or if MIR is unavailable when the subscriberunit exceeds its CIR, the system does not permit the subscriber unit toreceive or transmit data packets until the subscriber unit's informationrate falls back within a permitted level.

The CIR and MIR are established by agreement between the serviceprovider and the subscriber unit customer. For example, a subscribercustomer wishing to maintain the availability of 1.5 Mbits/sec isassigned a CIR of 1.5 Mbits/sec. The MIR may be set to 1.5 Mbits orgreater, depending on the agreement between the parties. Thus, assumingthe system's maximum information rate is 10 Mbits/sec, the MIR may beset anywhere from 1.5 Mbits/sec to 10 Mbits/sec.

If the subscriber unit has exceeded its CIR/MIR at 71, the access pointdrops the incoming Ethernet data packet. This typically does not resultin information loss, as the originating device typically re-sends thepacket. Processes for monitoring a subscriber unit's information rateand for comparing the information rate with CIR/MIR limits are discussedin detail below.

If the subscriber unit has not exceeded its CIR/MIR at 71, themicroprocessor places the incoming Ethernet packet in afirst-in-first-out buffer 73. When the packet passes through the buffer,the microprocessor constructs a radio frequency packet at 75 that willconvey the Ethernet packet to the subscriber unit. An exemplary RF datapacket structure is described in detail below. Briefly, however, andreferring also to FIGS. 18A and 18B, an RF data packet 66 is comprisedof a payload section 68, a MAC data packet header 70 and an RF preambleand header 72. The microprocessor forms payload section 68 and MAC datapacket header 70. A baseband processor 74 later forms RF preamble andheader 72

Payload section 68 is the entire Ethernet packet. MAC data packet header70 includes information used for routing and system management. It alsoincludes the SUID of a subscriber unit in the access point's sector thatwill next be allowed to transmit back to the access point. Themicroprocessor selects this subscriber unit through a polling algorithmat 76. The polling algorithm is described in detail below.

Upon forming the MAC data packet header, the microprocessor sends theheader and the payload to a field programmable gate array (FPGA) 78 oversystem bus 64. FPGA 78 includes parallel-to-serial conversion logic thatconverts parallel data from system bus 64 into a FIFO buffer 80 forserial output to baseband processor 74. The FPGA also includestransmit/control logic that controls operation of the baseband processorbased on the reception of packets by the FPGA. The FPGA initiatestransmit mode in the baseband processor and transmits packets to thebaseband processor at a time coordinated by the baseband processor.

Preferably, the baseband processor scrambles the MAC payload 68 and datapacket header 70. It then adds RF preamble and header 72 to the two MACpacket portions. The RF header provides information that, once thepacket is transmitted by the access point intermediate frequency (IF)modem 82, to enable the receiving subscriber unit's IF modem (not shown)to align its clock so that the packet's payload is properly received.That is, the present system initializes the transmission for eachpacket. A suitable baseband processor/IF modem pair is available fromIntersil Corporation of Irvine, Calif. (model numbers HFA 3783 and HFA3861B, respectively). It should be understood that various transmissiontechniques and arrangements may be utilized within the presentinvention. Such methods should be understood in this art and are,therefore, not discussed in further detail herein.

Baseband processor 74 converts the resulting RF packet into filtered Iand Q datastreams 84 and 86 in sending the packet to IF modem 82. Modem82 then modulates the I and Q datastreams onto an IF frequency andtransmits the packet to a half-duplex RF transceiver 88 at 90 overeither of a horizontally-polarized antenna array 42 or avertically-polarized antenna array 44. Since the RF packet isphase-modulated onto a carrier signal, the I (in-phase) and Q(quadrature) signals provide angle information by which modem 82 effectsthe modulation, as should be well understood.

In the embodiment described herein, IF modem 82 operates at a frequencyof approximately 480 mHz. Transceiver 88 upconverts the signal to thesystem's 5.8 GHz operational frequency. As indicated above, the accesspoint's operational frequency may be one of a plurality of channelswithin a range assigned by the Federal Communications Commission. Thepresent invention is not limited to frequency range and may operatewithin any suitable wireless environment.

Transceiver 88 transmits the RF preamble and header portion of the RFdata packet from antenna array 42 or 44 at one Mbit/sec BPSK andtransmits the MAC header and payload at eleven Mbits/sec QPSK. The lowerdata rate of the RF header facilitates the signal's capture by thereceiver's baseband processor in noisy environments. Once the basebandprocessor sets the clock for reception of the remainder of the packet,the higher information rate for that portion of the packet facilitatestransmission speed.

The access point may transmit data packets or command packets. A commandpacket has a structure similar to a data packet in that it has an RFpreamble and header, a scrambled packet header and a scrambled payload.Rather than data destined for a user device, however, the command packetincludes instructions for subscriber units for use in managing thesystem. A more detailed example of command and data packet structures isprovided below.

Regardless whether a packet transmitted by the access point is a commandpacket or a data packet, the packet's MAC header includes a transmitgrant, i.e. the SUID of the subscriber unit that next has permission totransmit to the access point. For example, assume the access pointreceives an Ethernet data packet destined for a user device attached toa subscriber unit A. Assume also that, according to the pollingalgorithm, a subscriber unit B is next eligible to transmit to theaccess point. The access point creates an RF data packet within which totransmit the data packet to subscriber unit A. Within the MAC header ofthis data packet, the access point microprocessor inserts the SUID ofsubscriber unit B into the transmit grant field. When transceiver 88broadcasts the RF data packet, all subscriber units in the accesspoint's sector monitor the transmission. Subscriber unit A, recognizingfrom the packet header that the payload in the data packet is intendedfor a user device attached to it, directs the packet to the intendeddevice. Subscriber unit B, although ignoring the payload, detects thetransmit grant in the data packet header and prepares to transmit to theaccess point.

A subscriber unit does not transmit to the access point unless itreceives a transmit grant. Thus, the access point only looks for asubscriber unit transmission during a period of time immediately afterthe access point transmits a packet. This wait period is related to thedistance between the access point and the subscriber unit and to theprocessing time needed by the subscriber unit to receive the transmitgrant and to generate and transmit a responsive packet. For example, apacket takes approximately 100 microseconds to travel round trip betweena subscriber unit and an access point that are ten miles apart. Assumingthat the delay created by processing within the subscriber unit rangesfrom 200 to 300 microseconds, the access point may preferably wait atleast 400 microseconds after issuing the transmit grant to receive aresponse from the subscriber unit.

Accordingly, following transmission of a data packet containing atransmit grant, each access point waits to receive a response from theidentified subscriber unit for a period of time based upon the distancebetween the access point and the farthest possible subscriber unit. Theaccess point is programmed for a maximum range within which subscriberunits will be disposed. The wait time is programmed into the accesspoint based on the furthest distance in this range. Thus, for example,where the maximum range from the access point is 10 miles, the wait timemay be set to 425 microseconds. Alternatively, the access point maydynamically set the wait time based on actual distances between thesubscriber units and the access point, changing the wait time as neededwhen new subscriber units are added in the sector and ranged by theaccess point as described below.

If each subscriber unit is programmed so that response to a transmitgrant takes precedence over all other activities, each subscriber unitcan be expected to consistently respond to an access point transmitgrant at the same period of time. Thus, if a subscriber unit responds ata different time, this may indicate that the subscriber unit has movedand is in need of re-authentication. Thus, the access point may providea notice of the change to the system administrator and, optionally, endall further communication with the subscriber unit until itsre-authentication.

The access point switches over to receive mode during the wait periodfollowing a packet transmission. In receive mode, antennas 42 and 44 arelinked to amplifiers in transceiver 88 at 90. The transceiver antennasdown-convert the signal received by the antennas from a subscriber unitto the IF frequency for IF modem 82. Modem 82 receives the signal andpasses its I and Q components 96 and 97 to baseband processor 74. If thesignal's energy level is above a predetermined threshold programmed intothe baseband processor (e.g. within a range of −80 dBm to −60 dBm), thebaseband processor initiates an automatic gain control loop with the IFmodem to bring the IF signal into an acceptable voltage range fordemodulation.

The baseband processor receives and decodes the preamble and header fromthe RF packet received from the subscriber unit, recovers the clock andaligns itself to receive the MAC data packet header and payload. Thebaseband processor de-maps the MAC data packet from I and Q symbols tobit patterns. Similarly to RF packets sent by the access point, MAC datapackets originating from the subscriber units are scrambled. Thebaseband processor de-scrambles the MAC data packet and clocks the datapacket out to FPGA 78 over a synchronous serial port. The FPGA convertsthe serial data to parallel, stores the parallel data in FIFO buffer 98and notifies microprocessor 60 that data has arrived. Microprocessor 60retrieves the data from the FPGA over system bus 64 and parses theoriginal Ethernet packet from the MAC data packet. As described in moredetail below, and similarly to MAC data packets built by the accesspoint, the MAC data packet from the subscriber unit is comprised of aheader and a payload, the payload being an Ethernet packet if the packetis ultimately destined for an Ethernet system. The microprocessorupdates the MAC-SU List (as described above with respect to FIG. 7B) at69, updates the subscriber unit's throughput usage at 71 and forwardsthe Ethernet packet across system bus 64 to Ethernet transceiver 58 andout through Ethernet port 48 to Ethernet switch 46 (FIG. 3) at 100.

The preceding discussion assumes that the subscriber unit responds to atransmit grant from the access point with a data packet. The subscriberunit responds to the transmit grant, however, whether or not thesubscriber unit has anything to send. If it has no outgoing data, thesubscriber unit responds with an RF packet enclosing a command packetthat returns the time stamp sent in the access point data packet. Thisnotifies the access point of the subscriber unit's continued existenceand operation in the system and allows the access point to operateaccording to the polling algorithm discussed below.

As noted above, and referring now to the functional diagram provided inFIG. 8, the subscriber unit architecture is similar to the access pointarchitecture shown in FIG. 5. A microprocessor subsystem 136 is shown asa single block with a microprocessor, DRAM and flash memory, but itshould be understood that this is a functional representation and thatthese components are discrete devices, as shown in FIG. 5. Accordingly,references below to “microprocessor 136” should be understood to referto the microprocessor within the subsystem. Similarly, Ethernettransceiver 56 is comprised of a physical layer component and a mediaaccess component.

Subscriber units may also be protected by shielding, indicated at 138 inFIG. 8. Baseband processor 74 and modem 82 are protected by shielding138, as are the components of transceiver 88, which are shown infunctional block diagram form. The subscriber unit transceiver'sarchitecture is the same as that of the access point transceiver.

When a user device attached to a subscriber unit attempts to communicatewith the Internet through the present system, the user device outputs avariable length Ethernet packet to the subscriber unit through the localarea network or direct Ethernet connection established between the userdevice and the subscriber unit. The Ethernet packets are received bymicroprocessor 136 from the Ethernet port. Microprocessor 136 transfersthe packets to the internal system DRAM and then forms a MAC data packetin a manner similar to that described above with respect to the accesspoint. The format of the MAC data packets created by the subscriber unitis different from that of data packets created by the access point.These differences are discussed in more detail below.

Microprocessor 136 sends the MAC data packet to FPGA 78. The FPGAdirects the parallel data packet into a FIFO buffer for serial output.

When the subscriber unit detects a transmission from the access pointwith the subscriber unit's SUID as the transmit grant, themicroprocessor activates the path to baseband processor 74 and outputsthe serialized MAC data packet to the baseband processor over asynchronous serial port. The baseband processor scrambles the MAC datapacket, adds the RF preamble and header control bytes, converts theresulting RF data packet into filtered I and Q data streams and sendsthe data to modem 82. The modem then modulates the I and Q data streamsonto an IF frequency. The RF transceiver up-converts the modulated IFfrequency to the transmission frequency and transmits the data throughantenna 38 or 40. Similarly to the access point, the subscriber unit maytransmit data packets or command packets.

When receiving a transmission from the access point, the subscriberunit's RF transceiver detects energy on antenna 38 or 40. Thetransceiver converts the signal's frequency to the IF frequency andoutputs I and Q data streams to baseband processor 74. If the energylevel of these signals is above a predetermined threshold, the basebandprocessor initiates an automatic gain control loop with modem 82 tobring the IF signal into an acceptable voltage range for demodulation.

The baseband processor first decodes the preamble and header to recoverthe clock, thereby aligning the baseband processor with the incomingtransmission. Similarly to the access point's baseband processor, thesubscriber unit baseband processor then decodes the MAC data packet andsends the resulting signal over a synchronous serial port to FPGA 78.The FPGA converts the serial data to parallel, stores the resultingsignal in a FIFO buffer, and notifies microprocessor 136 of the signal'sarrival. The microprocessor then retrieves the MAC data packet from theFPGA over a system bus and parses out the original Ethernet packet.Because the payload is an Ethernet packet, the microprocessor outputsthe packet through the Ethernet port (not shown) to the downstreamEthernet system that directs the packet to the destination identified inthe Ethernet packet header.

Where the unscrambled MAC packet header indicates that the packet is acommand packet, microprocessor 136 does not forward the packet to adownstream device but, instead, responds to the instructions in thecommand packet.

B. Polling Procedure

Returning to operation of the access point, transmission bandwidth isallocated to the subscriber units based on the subscriber units' use ofdata bandwidth. Initially, the term “bandwidth” is used elsewhere hereinto refer to a frequency range over which the access point and itssubscriber units communicate. As used here, however, “data bandwidth”refers the opportunity to communicate over all or part of that frequencyrange. For example, “data bandwidth” may refer to net data throughputper subscriber in Mbit/sec. The maximum data throughput capability ofthe system, in this case 10 Mbit/sec, is divided among all thesubscribers in the sector according to a set of rules by giving eachsubscriber a portion of a fixed, periodic time interval (one second, forexample) to use the radio frequency channel to receive or transmitpayload data. Thus, the description in the present example discussedherein of the access point allocating transmit or receive data bandwidthto the subscriber units refers to allocation of data throughput.

In the present example, the access point microprocessor selects the nextsubscriber unit to which to assign a transmit grant based on a pollingalgorithm designed to reduce system latency for typical traffic patternsin a multi-user networking environment. Very generally, latency may beconsidered the delay in communications arising from the operation of theaccess point and subscriber units. That is, and referring to FIG. 3, ifa baseline time is considered to be the time required for communicationbetween Ethernet switch 46 and user device 34 over a hard wireconnection, system latency is the difference between the baseline timeand the time required for communication between those points throughaccess point 18 and subscriber unit 22. In the present example, verylittle latency is introduced in communications from the access point tothe subscriber units, since the access point simply passes incomingEthernet packets to their desired destinations as they arrive, subjectto CIR/MIR limitation.

Upstream traffic, however, requires a different type of decisionregarding which communications will be permitted at a given time. Forexample, an access point may define a designated period of time, or“contention” period, following downstream transmissions in whichsubscriber units may transmit. During the contention period, the accesspoint moves into receive mode for receipt of a transmission from asubscriber unit. In the present embodiment, however, the access pointselects the order in which subscriber units may transmit without the useof a contention period. Thus, the primary source of latency for upstreamtraffic is the period between transmit grants assigned by the accesspoint.

The polling algorithm defines the order in which subscriber units areselected for a transmit grant. Priority in the polling algorithm may beassigned on a constant basis through agreement between the subscriberunit operator and the service provider. For such subscriber units, thepolling algorithm assigns priority regardless of the subscriber units'need to transmit. Outside this group, however, a subscriber unit'stransmit priority increases or decreases based on how frequently thesubscriber unit uses the system. This allocates bandwidth to subscriberunits more likely to need bandwidth without wasting time monitoringlesser active subscriber units, thereby improving the latency that themore-active subscriber units might otherwise experience.

The system defines bandwidth priority in part through timers assigned tothe subscriber units. In the present example, timers are assigned to thesubscriber units in groups that are utilized by the polling algorithm toallocate transmit grants. The groups are maintained in memory at theaccess point. The access point maintains a list of subscriber unit SUIDsassociated with each polling group, and the access point microprocessordynamically assigns subscriber units to the different groups based atleast in part on data demand. The groups contain other information asdiscussed below.

Referring to FIG. 9, the polling timer for each polling group, exceptgroup zero, has an expiration period that varies with the number ofsubscriber units in the group. As described in more detail below, theaccess point microprocessor repeatedly checks the timer of each group todetermine whether any action should be taken with the subscriber unitsin the group. Thus, in general, the length of a timer's expirationperiod is inversely related to the preference the group receives fromthe microprocessor. That is, the microprocessor deals more frequentlywith subscriber units in groups having shorter polling timers than thosewith longer timers.

Timer length varies with the number of subscriber units in the group.When the microprocessor polls a group, it will act only on onesubscriber unit in the group before moving to the next group. Thus, aseach additional subscriber unit is added to the group, the timer lengthis reduced so that the latency experienced by each individual subscriberunit is approximately the same as if it were the only subscriber unit inthe group.

Referring to group two in FIG. 9, for example, the group's initial timerlength is 60 ms. This will be the timer length if there are zero or onesubscriber units in the group. In this case, the microprocessor pollsgroup two no more than once every 60 ms. If group two includes twosubscriber units, the timer length changes to 40 ms. While themicroprocessor now polls group two more frequently, the existence of twosubscriber units in the group means that the microprocessor acts on anindividual subscriber unit in the group only every other poll. Thus,from the perspective of a given subscriber unit, the polling frequencygoes to 80 ms from 60 ms.

The initial timer length (T_(max)) is the maximum timer length a groupexperiences. There is also, however, a minimum timer length (T_(min)).Regardless how many subscriber units are contained in group two, forexample, the actual timer length (T_(poll)) does not drop below 20 ms.T_(poll) varies according to rules based on the number of subscriberunits (NS) in the group. For groups one through six and eight, if NS isless than 127, thenT _(poll)=(T _(max) −T _(min))/(NS)+T _(min).If NS is greater than or equal to 127, thenT_(poll)=T_(min).For group seven, if NS is less than 11, and if T_(min) is less than orequal to (T_(max))/(NS), thenT_(poll)=(T_(max))/(NS).If NS is less than 11, and if T_(min) is greater than (T_(max))/(NS),thenT_(poll)=T_(min)If NS is greater than or equal to 11, thenT_(poll)=T_(min).

Accordingly, with zero or one subscriber units, timer length is at itsmaximum level assigned to the group. As subscriber units are added,timer length decreases until reaching the timer length minimum.Regardless how many subscriber units are thereafter added to the group,timer length remains the same.

The microprocessor also controls placement of subscriber units in thevarious groups. With the exception of subscriber units assigned to groupseven, a subscriber unit can belong to only one group at a time. Groupseven is a fixed latency polling group. By agreement with the serviceprovider, these subscribers may be guaranteed at least a minimumlatency—i.e., at least a minimum subscriber unit polling period when thenumber of subscriber units in the group is less than eleven. Anysubscriber unit covered by such an agreement is placed in group sevenfollowing its authentication in the system and remains there as long asit remains active. These subscriber units, along with all othersubscriber units, also enter the polling sequence comprising groups zerothrough five.

At system start-up, all subscriber units reside in group eight. Asindicated in FIG. 9, the microprocessor polls group eight every fiveseconds, or up to every 100 milliseconds, depending on the number ofsubscriber units in the group. Referring also to FIG. 10, when themicroprocessor polls group eight at 140, it first checks at 142 whetherthe table for group eight has more than ten subscriber units. If not,the microprocessor moves a pointer at 144 to the next subscriber unit inthe list and checks at 146 whether the subscriber unit has yet beenauthenticated.

Authentication is the recognition by the access point that thesubscriber unit exists and is operating in the access point's sector.When the subscriber unit is installed in the sector, the system operatormakes an entry for the subscriber unit in the static subscriber unitdatabase stored in the access point's flash memory 61 (FIG. 5). For eachsubscriber unit, the operator enters an SUID (e.g., a number assigned bythe operator), the subscriber unit's MAC address, the subscriber unit'sattribute (i.e., whether it is a priority or regular subscriber unit forpolling purposes) and the subscriber unit's rated CIR and MIR. Theaccess point uses the stored database to initialize a dynamic databasethat is updated during the system's operation. The dynamic databaseincludes the data for the various tables described herein. Thus, forexample, the various group tables are lists of SUID's that point to datain the dynamic database.

When the subscriber unit is entered in the database, the microprocessoradds the subscriber unit to the group eight list. At this point, thesubscriber unit is not authenticated, since it has not received andresponded to an authentication packet from the access point. Thus, whenthe microprocessor examines the entry for the subscriber unit in thegroup eight table at 146, it sees that the subscriber unit has not beenauthenticated, and, at 148, creates an authentication request commandpacket requesting the SU with an SUID matching the SUID in the transmitgrant field to reply with it's hardcoded Ethernet MAC address. Thepacket goes into FIFO buffer 80 (FIG. 4) for transmission, and themicroprocessor exits the group eight routine at 150 to the next step inthe polling algorithm.

After the access point transmits the command packet, it should receivein the following wait period a return command packet from the subscriberunit with a payload carrying the subscriber unit's MAC address. If thismatches a MAC address stored in the access point's SU database for thatSUID, the microprocessor updates the entry for that subscriber in thegroup eight table to indicate the subscriber unit has been authorized.If the subscriber unit is authenticated at 148, the microprocessor movesthe subscriber unit to group six at 152.

The microprocessor leaves the software pointer at the subscriber unit atsteps 148 and 152. When the microprocessor returns to group eight in thepolling algorithm, the microprocessor examines the next subscriber unitat 146.

Group eight contains not only new subscriber units, but also existingsubscriber units that fail to respond to a transmit grant. That is,group eight holds all subscriber units that have been entered in theaccess point database but that are inactive or not yet authenticated.Accordingly, particularly when multiple subscriber units go off-line, itis possible that group eight may contain several subscriber units. Thus,if group eight contains more than ten subscriber units in its list at142, the microprocessor scans the group eight list and selects at 154the four subscriber units that have most recently been sentauthentication packets.

Examining the entry in the group eight list for the previous foursubscriber units, the microprocessor checks the entry at 156 to see ifthe subscriber unit responded with a valid MAC address. If so, themicroprocessor moves the subscriber unit to group six at 158 and movesto the next of the four subscriber units at 154. If the subscriber unithas not responded to the authorization packet at 156, the microprocessormoves to the next of the four subscriber units at 154. A temporarypointer is used to move through the four subscriber units and is deletedupon completion of the search.

Returning to FIG. 9, group six is an intermediate position between groupeight and the data polling groups, i.e. groups seven and groups zerothrough five. Prior to forwarding the subscriber units to the datapolling groups, the access point confirms their range and RF signalpower level through command packets sent to the subscriber units. Thecommand packet includes a time stamp applied by the access point, thedesired subscriber unit's SUID as the transmit grant, and a power levelchange instruction. The subscriber units are programmed to immediatelyrespond to this request. Thus, during the access point's following waitperiod, the subscriber unit responds with a command packet echoing theaccess point's time stamp. By comparing the time stamp with the time atwhich the access point receives the return packet, the access pointmicroprocessor determines the distance between the access point and thesubscriber unit. If the power level change instruction is non-zero, thesubscriber unit adjusts its output power according to the instruction.

Generally, the ranging/power leveling process is comprised of fivecycles of six ranging/power leveling packets sent by the access point toa subscriber unit. Within each cycle, the access point determines therange and power level of each response from the subscriber unit anddetermines the maximum calculated range and the maximum power levelmeasured at the access point for the six responses. In the last packetin each cycle, the access point issues a power level change command toincrementally increase and decrease, as appropriate, the subscriberunit's output power level toward a desired level.

As shown in FIG. 9, the access point microprocessor polls group six atmost once every 90 ms if there are zero or one subscriber units in thegroup. The microprocessor polls the group more frequently if there aremore subscriber units, to a minimum rate of once every 8 ms.

FIG. 11 illustrates the procedure executed by the microprocessor inpolling group six. As with group eight, group six is defined as a listof subscriber units in memory. The list includes the SUID for eachsubscriber unit, the maximum power level measured by the basebandprocessor from all past power leveling responses received from thesubscriber unit during the present six-request cycle, the power level ofthe last response in the cycle, the minimum average and maximum rangesdetermined in the cycle, and the last range determined in the cycle.Each entry also includes a ranging/power leveling timer (a time stamp oflast ranging or power leveling response plus a fixed interval, forexample 100 ms, at which the timer will expire).

At 160, the microprocessor moves sequentially through the next fivesubscriber units in the list of subscriber units in group six, examiningthe ranging/power leveling timers of each. The access point checks eachtimer value to determine if it has expired (i.e., if it is older thanthe current time). If none of the subscriber unit timers has expired at164, the microprocessor exits the group six poll at 186. If themicroprocessor finds a subscriber unit among the five under examinationat 164 for which the timer has expired, the microprocessor places apointer at the subscriber unit and checks at 166 to see if thesubscriber unit has completed all five ranging/power leveling cycles. Ifso, then power leveling is complete for this subscriber unit, and themicroprocessor checks at 168 to determine whether the subscriber unit isa priority subscriber pursuant to an agreement with the serviceprovider. If so, the microprocessor assigns the subscriber unit to groupseven at 170 and to group four at 172. That is, as described above, thesubscriber unit is placed both in the priority group seven and in thevariable groups zero through five. The microprocessor then moves thepointer to the next subscriber unit and exits the group six poll at 174.

If the microprocessor has not yet completed the ranging/power levelingcycles at 166, the access point checks a “ping response” timer for thesubscriber unit at 176. This timer, which is discussed below, providesan indication whether the subscriber unit has responded to previouspackets sent by the access point. If the subscriber unit has failed torespond, or has responded beyond a certain time limit so that it may beconsidered off-line, the microprocessor moves the subscriber unit backto group eight at 177 and exits the group six poll at 174.

If the subscriber unit responds to the poll at 176, the microprocessorchecks at 178 to see if the subscriber unit is at the end of asix-request cycle. If not, the access point creates a ranging requestpacket at 186 and sends the packet to the subscriber unit. As the packetis for a range request, the power leveling change instruction is zero.The access point leaves the database pointer on this subscriber unit andexits the group six poll at 184.

When the access point receives a packet from the subscriber unit inresponse to the ranging packet sent by the access point at 186, theaccess point updates the time stamp for the subscriber unit'sranging/power leveling timer and stores the range calculated from theresponse packet's time stamp. If the received power level is greaterthan the current power level value, the access point also stores thereceived power level as the subscriber unit's power level value.

Because the pointer remains at the same subscriber unit, it is the firstof the subscriber units examined at 160 at the next group six poll. Ifthe subscriber unit's timer has expired, the access point checks againat 178 whether the ranging/power leveling sequence is at the last of thesix requests in a cycle. If so, the access point calculates at 180 anincremental increase or decrease for the output power level of thesubscriber unit's transceiver 88 (FIG. 8) based on the differencebetween the desired power level and the value in subscriber unit's powerlevel field, i.e., the maximum power level from the previous fiveresponses. If the difference is greater than 4 dB, the increment (eitherpositive or negative) is equal to 4 dB. If the difference is less than 4dB, the increment is equal to the difference.

At 182, the access point sends a command packet to the subscriber unitwith an instruction to change the subscriber unit's power output levelby the increment determined at 180. The access point leaves the pointeron this subscriber unit and exits the group six poll at 184. When theaccess point receives a packet from the subscriber unit in response tothe power leveling packet sent by the access point at 182, the accesspoint updates the time stamp for the subscriber unit's power levelingtimer and stores the received power level in the table as the last powerlevel value. If this power level is also the greatest power level overthe last six responses, it is also stored as the maximum power level.

As indicated in FIG. 11, and returning to FIG. 9, the microprocessorapplies all subscriber units completing the ranging and power levelingprocedures to group 4. If a subscriber unit is also a “priority”subscriber, the microprocessor also places the subscriber unit in group7. The microprocessor assigns transmit grants based on the presence ofsubscriber units in groups zero through five and seven. Thus, once asubscriber unit enters these groups, it is eligible to receive atransmit grant. Downstream data from the AP to the SU does not require atransmit grant but will be filtered by the CIR/MIR manager.

The access point microprocessor sequentially polls these groups inreverse numerical order. That is, the microprocessor polls group sevenand then groups five through zero. At each poll, the microprocessorfirst checks to see whether the group's polling timer has expired. Asdescribed above, the polling timer has a default maximum value that candecrease, depending on the number of subscriber units in the group, to aminimum value. If the timer has not expired, the microprocessor moves tothe next group. If the timer has expired, the microprocessor looks tosee if any subscriber units are in the group. If the group containssubscriber units, the microprocessor looks for a subscriber unit havingavailable CIR or MIR. If none are present, the microprocessor moves tothe next group. If such a subscriber units exists, the microprocessorselects its SUID as the transmit grant for the next outgoing RF datapacket. The microprocessor then resets the polling routine.

By beginning the routine at group seven, the microprocessor provides agreater degree of certainty that group seven will be polled promptlyupon expiration of its timer. By thereafter beginning the remainder ofthe poll at group five, and moving sequentially up to group zero, themicroprocessor provides the opportunity to first poll those groups withlonger polling timers.

The microprocessor moves subscriber units among groups zero through fivedepending on the frequency of their transmission of data to, and receiptof data from, the access point. As described above, every time an activesubscriber unit detects its SUID in a transmit grant, it responds to theaccess point. If the subscriber unit has nothing to transmit, it simplyechoes with a command packet enclosing its SUID and the access point'stime stamp. Such echoes are not considered for polling status purposes.On the other hand, if the subscriber unit has a data packet fortransmission to the access point, the subscriber unit transmits the datapacket responsively to receipt of its transmit grant. The pollingalgorithm does consider these transmissions. Similarly, the pollingalgorithm does not consider command packets sent by the access point tosubscriber units but does consider data packets.

The access point tracks the receipt of data packets from, and thetransmission of data packets to, its subscriber units. Specifically, theaccess point status table includes a “last traffic time stamp”—a timestamp indicating when the last data packet was transmitted to orreceived from a subscriber unit. When a subsequent data packet istransmitted in either direction between the access point and the samesubscriber unit, the access point overrides the earlier time stamp.

Each time the microprocessor updates the subscriber unit's last traffictime stamp, the microprocessor also moves the subscriber unit up in thepolling sequence, as shown in FIG. 9. Generally, a subscriber unit movesup two groups at a time, the exception being from group one to groupzero. Thus, if a data packet is transmitted between the access point anda subscriber unit in group five, the microprocessor moves the subscriberunit to group three. Subscriber units move from group three to group oneand from group one to group zero. If the access point transmits orreceives a data packet to or from a subscriber unit in group four, themicroprocessor moves the subscriber unit to group two. Under similarcircumstances, subscriber units move from group two to group zero.

If the access point does not receive a data packet from or transmit adata packet to a subscriber unit in any of groups zero, one, two, three,or four within a predetermined interval, the microprocessor moves thesubscriber unit down one group. The predetermined interval varies witheach group, as shown in FIG. 9. Thus, if a subscriber unit in group zerohas no data packet traffic for 100 ms, the subscriber unit drops togroup one. A subscriber unit in group one that has no data packettraffic within a 500 ms period drops to group two. The timers for groupstwo, three, and four are two seconds, two minutes, and thirty minutes,respectively.

The access point also maintains a “ping response” time stamp that isupdated each time the access point receives a response packet from thesubscriber unit, regardless whether the response is a command packet ora data packet. From time to time, the microprocessor determines thedifference between the present time and the ping response time stamp. Ifthe access point fails to receive any response from a transmit grantissued to a subscriber unit in a 300 second period in any of groups onethrough seven, the microprocessor moves the subscriber unit to groupeight under an assumption that the subscriber unit has gone offline. Ifthat is not the case, or if the subscriber unit is thereafter placedback online, the subscriber unit moves to group six and on to the datapolling groups as described above. Accordingly, the polling groups shownin FIG. 9 completely describe the possible polling status of allsubscriber units associated with the access point.

As described above, each subscriber unit is associated with a committedinformation rate (CIR) and a maximum information rate (MIR) that areestablished by agreement with the service provider and that areconsulted before the access point conveys any Ethernet traffic to orfrom a subscriber unit in the form of an RF packet transmission.Similarly, the access point microprocessor also consults CIR/MIR limitsat the polling operation 76 (FIG. 4) in determining whether a subscriberunit is eligible for a transmit grant. Thus, CIR/MIR limitations affecta subscriber unit's ability both to receive and transmit data and,therefore, affects the subscriber unit's position in the polling groups.

During the polling algorithm, and referring to FIG. 12, themicroprocessor only checks CIR and MIR for subscriber units in groupszero through five and group seven, since transmit grants for datapackets are provided only for subscriber units in those groups.Generally, FIG. 12 reflects the sequence in which the microprocessorseeks to poll groups zero through eight. At the beginning 188 of thetransmit grant polling routine at 76 (FIG. 4), the microprocessor checksat 190 to determine whether the polling timer for group eight hasexpired. If so, the microprocessor checks at 192 whether any subscriberunits are present in the group. If so, the microprocessor executes thepolling routine (FIG. 10) for group eight at 194. Upon completing thepolling routine, or if no subscriber units are present in group eight at192, or if the group eight timer has not expired at 190, themicroprocessor checks the polling timer for group six at 196.

If the group six timer has expired, the microprocessor checks at 198 todetermine whether any subscriber units are present in the group. If so,the microprocessor executes the polling routine (FIG. 11) for group sixat 200. Upon completing the polling routine, or if no subscriber unitsare present in group six at 198, or if the group six timer has notexpired at 196, the microprocessor checks at 202 whether a data packetis ready from RF packet constructor 75 (FIG. 4).

If the RF packet constructor is empty at 202, this means there are nodata packets ready for a transmit grant. The microprocessor then checksat 204 whether any packets are ready for immediate transmission in RFtransmission FIFO buffer 80 (FIG. 4). If so, the microprocessor returnsto the beginning of the polling algorithm at 188.

If there are no packets in either packet constructor 75 or transmissionbuffer 80 (FIG. 4), the access point creates a short “ping” packet at206 to assure that the access point transmits an outgoing packet with atransmit grant. In this way, the access point assures that it repeatedlygives subscriber units an opportunity to transmit back to the accesspoint and update the subscriber unit's ping response time stamp. Theping packet has a time stamp and a transmit grant, as determined by thepoll of groups seven through zero, but otherwise has no subscriber unitdestination address or payload.

If there is an outgoing packet ready in packet constructor 75 (FIG. 4)at 202, or if the access point has created a ping packet at 206, themicroprocessor checks at 208 to determine whether the polling timer forgroup seven has expired. If so, the microprocessor examines the group at210 to determine whether any subscriber units are present in the group.If so, the microprocessor executes the polling routine (FIG. 13) forgroup seven at 212. If the group seven routine returns a subscriber unitaddress at 214 eligible for a transmit grant, the microprocessor assignsthe subscriber unit's SUID as the packet's transmit grant at 216 andmoves the packet to transmission buffer 80 (FIG. 4). The microprocessorthen returns to the beginning of the polling routine at 188.

If no such subscriber unit exists in group seven at 214, or if groupseven has no subscriber units at 210, or if the group seven timer hasnot expired at 208, the microprocessor checks the timer for group fiveat 218. The procedure repeats for group five and, provided no acceptablesubscriber units are found, sequentially repeats for groups four, three,two, and one. If the group one timer has not expired at 220, or if nosubscriber units are present in group one at 222, or if the pollingroutine for group one at 224 provides no eligible subscriber units at226, the microprocessor moves directly to group zero without checking atimer. Thus, the microprocessor always checks group zero if it passesthrough the other groups without finding an acceptable subscriber unit.If group zero produces an acceptable subscriber unit, its SUID isattached as the outgoing packet's transmit grant at 216. If not, themicroprocessor sends the packet to transmission buffer 80 (FIG. 4)without a transmit grant at 228 and returns to the beginning of thepolling routine at 188.

FIG. 13 illustrates the execution of polling routine 212 for groupseven. At 230, the microprocessor begins a scan of all subscriber unitsin group seven. Like groups zero through five, group seven includes alist of SUID's. For each SUID, there are two pieces of data used fromthe dynamic database: last traffic time stamp and ping response timestamp. The subscriber units are indexed in each table in the order inwhich they were authenticated by the access point.

Initially, a software pointer is associated with the first subscriberunit in the group seven list. At 230, the microprocessor begins withthis subscriber unit and checks its ping response time stamp at 232. Ifthe time stamp is too old, the microprocessor moves the subscriber unitto the group eight list at 234, moves the software pointer to the nextsubscriber unit at 236, and returns to 230 to examine this subscriberunit.

If the subscriber unit's ping response time stamp indicates at 232 thatthe subscriber unit responded to its last transmit grant, themicroprocessor checks the availability of CIR and MIR for the subscriberunit at 238. If CIR/MIR is unavailable, the microprocessor moves thesoftware pointer to the next subscriber unit at 236 and returns to 230to examine the next subscriber unit.

If the microprocessor passes through all subscriber units in the groupseven list without finding an acceptable subscriber unit at 232 and 238,the software pointer is left again at the initial subscriber unit, andthe microprocessor returns a negative response at 240 to step 214 inFIG. 12. If the microprocessor finds an eligible subscriber unit atsteps 232 and 238, it selects its SUID at 242 and returns the SUID at240 to step 214 in FIG. 12. The microprocessor also moves the softwarepointer to the next subscriber unit in the list. Thus, themicroprocessor begins with this subscriber unit at the next pass throughgroup seven.

FIG. 14 illustrates the execution of the polling routine for group five.It is the same as the group seven routine, except that themicroprocessor only scans the first five subscriber units in the list,beginning with the next subscriber unit after the one at which thesoftware pointer is located upon entry into the search. If themicroprocessor fails to find an eligible subscriber unit at steps 232and 238 among this subset of five subscriber units, it exits the routineat 240. If the microprocessor finds an eligible subscriber unit, itreturns that subscriber's SUID at 242, then exits at 240.

FIG. 15 illustrates the execution of the polling algorithm for each ofgroups one through four. It is the same as the group five routine,except that between the offline check and the CIR/MIR check, themicroprocessor checks the subscriber unit's last traffic time stamp at244. Because the microprocessor replaces a subscriber unit's lasttraffic time stamp every time the access point receives or transmits adata packet from or to the subscriber unit, the difference between thepresent time and the last traffic time stamp is a measure of howrecently the subscriber unit has required data bandwidth. If thesubscriber unit has not used data bandwidth within the time limit (seeFIG. 9) for the particular group, the microprocessor moves thesubscriber unit down one group at 246.

Additionally, if CIR and MIR are unavailable for a subscriber unit at238, and if the subscriber unit is in groups one or two, themicroprocessor moves the subscriber unit down one group at 246.

FIG. 16 illustrates the execution of the polling algorithm for groupzero. It is the same as the routine for groups one through four,primarily except that the microprocessor reviews all subscriber units,not just the first five, until finding an eligible subscriber unit.Additionally, if CIR and MIR are unavailable for a subscriber unit at238, the subscriber unit is moved down to group two at 246.

C. CIR/MIR Management

FIG. 17 illustrates the procedure executed by the microprocessor inchecking for CIR/MIR availability, which the microprocessor determinesfrom information maintained by the microprocessor at the access pointdatabase. Each subscriber unit status table entry has “CIR remaining”and “MIR remaining” entries. The last traffic time stamp is also usedand is referred to in this discussion as the “IR time stamp.” At systemstartup, the microprocessor initializes the IR time stamps of allsubscriber units. That is, all subscriber units have approximately thesame time stamp. The CIR remaining entry begins as the subscriber unit'srated CIR value, while the MIR remaining value starts as the differencebetween the rated MIR value and the rated CIR value. For example, assumethat a subscriber unit's rated CIR value is 1.5 Mbits/sec and that itsMIR is 10 Mbits/sec. When the microprocessor updates the CIR/MIRremaining values in the subscriber unit's slot in the status table, theCIR is 1.5 Mbits/sec, and the remaining MIR is 8.5 Mbits/sec.

The microprocessor decrements the status table entry's CIR value eachtime the access point transmits a data packet to, or receives a datapacket from, the particular subscriber unit. Command packets do notcount against CIR usage. If CIR has been completely used (i.e., the CIRvalue in the status table is zero), the microprocessor decrements MIR.If MIR is also depleted, the microprocessor leaves both values as zeroand drops the packet.

When the microprocessor receives an Ethernet packet from Ethernet switch46 (FIG. 3) and finds a destination subscriber unit in the MAC addresstable, the microprocessor decrements CIR (or MIR, if CIR has expired)for that subscriber unit in the status table by the number of bits inthe Ethernet packet's payload. Similarly, when the access point receivesan RF packet for a subscriber unit and parses out an enclosed Ethernetpacket to the Ethernet switch, the access point microprocessordecrements the subscriber unit's remaining CIR or MIR.

Referring again to FIG. 4, the access point checks CIR/MIR availabilitytwice: (1) when receiving an Ethernet packet destined for a user deviceat 47, and (2) when selecting a subscriber unit for a transmit grant at76. In the first instance, the access point checks CIR and MIR to see ifa subscriber unit is eligible to receive a given packet currently in thesystem. In the second instance, the access point prospectively checksCIR/MIR so that the subscriber unit selected for a transmit grant cantransmit a packet within its CIR/MIR limits.

Referring to FIG. 17, when the access point receives a packet fromEthernet port 46 (FIG. 3) the access point microprocessor searches theMAC-SU List at 248 for the subscriber unit address associated with thepacket's destination MAC address, as described above. If the SUID is notfound at 250, the microprocessor checks an Ethernet broadcast filter at252.

As should be understood in this art, an access point may receive variouspacket types. Certain higher-level protocols make use of broadcast-typepackets. These packets are not addressed to a signal destination device,but instead request that they be sent to all (broadcast) or some(multicast) destinations in the access point's sector. It is possiblethat an excessive number of such packets, particularly if receivedduring periods of high traffic, could slow system performance.Accordingly, the access point maintains an Ethernet broadcast “filter”as a decision block at 250 in the routine shown in FIG. 17 thatdetermines whether to forward broadcast packets. Thus, the operator mayallow or prohibit Ethernet broadcast and multicast packets, depending onsystem needs. In the presently described embodiment, the Ethernetbroadcast filter does not affect broadcast of ARP broadcast packets.

If the broadcast filter is disabled at 250, the access point sets thedestination address for the resulting RF packet at 254 to broadcast thepacket to all subscriber units and sends the packet to Ethernet payloadFIFO 73 (FIG. 4) at 256. If the filter is enabled, the microprocessordetermines whether the broadcast packet is an address resolutionprotocol (ARP) packet at 258. If not, the access point drops the packetat 260.

As should be well understood, an ARP packet is a type of Ethernetpacket. An Ethernet packet typically has source and destination MACaddresses. When a user device, such as a personal computer, initiates acommunication with a system for which the PC has an IP address, but nota MAC address, the PC may transmit an ARP packet requesting adestination address. The destination device receives the ARP packet andresponds with an ARP packet having the destination MAC address or asecure version of it.

When a user device is initially installed, it does not know the MACaddresses of destination devices with which it may need to communicate.Thus, its initial transmission through the access point will be an ARPpacket, and the initial packet coming back through the Ethernet port forthe user device will be a responsive ARP packet. The responsive ARPpacket has the user device's IP address, but not its MAC address, andthe access point therefore needs to broadcast the ARP packet to allsubscriber units. As described above, the user device's subscriber unitresponds to the broadcast, and the access point adds this relationshipto the MAC-SU List.

Downstream broadcast packets do not count against subscriber unitCIR/MIR. All forms of broadcast packets count against CIR/MIR, however,if they come upstream from a subscriber unit.

When a subscriber unit is selected for a transmit grant, or when theaccess point receives a data packet from a subscriber unit, or when theaccess point finds the subscriber unit SUID for an incoming Ethernetpacket at 250, the microprocessor checks the subscriber unit's IR timestamp at 262. As described above, a subscriber unit's information rateis measured over a one-second look back. If the subscriber unit's IRtime stamp is over one second old, the look-back period has expired, andthe microprocessor updates the IR time stamp, the CIR value and the MIRvalue in the status table at 264. That is, the microprocessor replacesthe old IR time stamp with a current time stamp and resets the remainingCIR and MIR for the subscriber unit with the subscriber unit's rated CIRand rated CIR/MIR differential.

If the time stamp has not expired at 262, the microprocessor checks theCIR status for that subscriber unit at 266. If the CIR is greater thanzero, the microprocessor decrements the remaining CIR value in thestatus table by the number of bits in the data packet's payload or, ifthe number of bits is greater than the remaining CIR, sets the CIR tozero and, at 256, (1) sends the Ethernet packet to buffer 73 (FIG. 4),or (2) sends the required RF packet to receive buffer 98 (FIG. 4), or(3) assigns the subscriber unit's MAC address as the transmit grant inthe next outgoing packet, as appropriate. If the CIR check is forselection of a transmit grant, step 268 is omitted. The microprocessorexits the routine at 270.

If the CIR check is for an upstream data packet received from asubscriber unit, and if the CIR is zero at 266, the microprocessor exitsthe routine and processes the packet. If the CIR check is for a transmitgrant or a downstream packet, and if CIR is zero at 266, themicroprocessor checks the status table at 272 to see if the subscriberunit's MIR is greater than zero. If not, the microprocessor drops thedownstream packet at 260, or indicates in a transmit polling routinethat no CIR/MIR is available, as appropriate. If MIR is available, themicroprocessor checks at 274 to determine whether the MIR threshold isenabled.

The MIR threshold is programmable by the system operator, who maycommunicate with and control the access point through any suitablemeans, for example a hyper-terminal connection or a telnet session. TheMIR threshold is a measure of system usage above which MIR will not beavailable to the subscriber units.

If the MIR threshold is enabled, the microprocessor monitors the overallsystem information rate on a one-second look back each time a packetcomes in from the RF receiver or a packet comes into the Ethernet port.For example, assume that the overall system capacity is 10 Mbits/sec andthat the default MIR threshold is 6 Mbits/sec. Unless the operatordisables the MIR threshold, the microprocessor monitors the overall datatraffic through the access point on a second-by-second basis. If thetotal information rate rises above the threshold, the access point nolonger permits outgoing traffic for any subscriber unit, or theassignment of a transmit grant to any subscriber unit, based on MIRcapacity. Thus, as system capacity grows, the MIR threshold inhibitsexcessive MIR use to the detriment of CIR use.

If the MIR threshold is enabled at 274, the microprocessor checks thethreshold at 276 to determine whether system traffic has exceeded thethreshold. If not, then the subscriber unit's MIR is available, and themicroprocessor takes the appropriate action at 268 and/or 256. If systemusage exceeds the MIR threshold at 276, the microprocessor drops thepacket at 260, or indicates in a transmit polling routine that noCIR/MIR is available, as appropriate.

D. Packet Arrangement

FIGS. 18A and 18B illustrate an exemplary structure for packets passingdownstream from the access point to a subscriber unit. As indicatedabove, packets may be described generally as either command packets ordata packets. Data packet 66 is described generally above. It includesan RF preamble and header 72, a scrambled MAC data packet header 70, anda scrambled payload 68. The MAC data packet header has several fields. Asource access point ID 270 is the MAC address for the access point. AMAC data packet length 272 is the length of the MAC data packet,including the data packet header and the payload. A transmit grantsubscriber unit ID 274 is the MAC address of the subscriber unit chosenfor the next transmission slot through the polling algorithm.

A packet header checksum field 276 includes checksum bits for use by thedownstream subscriber unit. The subscriber unit, upon receiving the RFdata packet, counts the number of bits in the MAC data header and thepayload. The last four bytes of this sum should match the number inchecksum field 276. If it does, the subscriber unit accepts the packet.If not, it is assumed that there has been a transmission or receptionerror, and the subscriber unit drops the packet. The use of checksumsshould be well understood in this art.

As described above, each received Ethernet packet includes a destinationMAC address and a payload. The access point microprocessor locates thesubscriber unit SUID from the MAC-SU List corresponding to the Ethernetpacket's destination address and places it into field 280. The accesspoint microprocessor also supplies transmission grant subscriber SUID274, packet header checksum 276, access point ID 270, and data packetlength 272. The Ethernet packet itself goes to payload 68.

Because payload 68 is relatively large (in this example, 1,600 bytes),it may be possible to fit multiple Ethernet packets into a single RFdata packet payload within the 1600 byte capacity. Thus, themicroprocessor reads the length of each incoming Ethernet data packetand combines these packets, up to a maximum of four Ethernet datapackets, into a single RF data packet payload. Accordingly, MAC datapacket header 70 includes four pairs of payload header fields280A/282A-280D/282D, each including the subscriber unit destination ID280 and the length 282 of a corresponding section 284 of payload 68 thatcontains the applicable Ethernet data packet.

For example, suppose the access point transmits a data packet havingfour payloads destined for four different subscriber units. Since allsubscriber units in the access point's sector receive all transmissionsfrom the access point, each of the four subscriber units read its SUIDin the MAC data packet header. By reading the payload lengths 282A-282D,the subscriber unit microprocessor knows the position of its payloadwithin payload section 284A-284D. Thus, the subscriber unit is able toparse out its Ethernet data packet from the overall RF data packetpayload 68.

Command packets are in the form as indicated at 286. The command packetincludes an RF preamble and header 288 that is identical to the RFpreamble and header 72 of the RF data packet. Like the RF data packet,the command packet portion is scrambled and is comprised of a commandpacket header 288 and a command payload 290. Command packets aregenerated by the access point and are used for various functions, forexample to provide firmware updates and to issue ranging and powerleveling commands.

As with the MAC data packet header, the command packet header isconstructed by the access point microprocessor. It includes a sourceaccess point identification field 292, a command packet length field294, a destination subscriber unit identification field 296, a commandfield 298, a transmission grant subscriber unit SUID 300, and a packetheader checksum field 302. Source access point identification field 292,transmit grant subscriber unit identification field 300, and checksumfield 302 are similar to the corresponding fields in the data packet.Unlike the data packet, however, the transmit grant might not bedetermined from the polling algorithm. In authentication and rangingpackets, for example, the transmit grant ID is the same as thesubscriber unit destination 10. For firmware upgrades, however, thepolling algorithms are used to determine transmit grant. Generally, thetransmit grant field of a command packet will depend on the purpose ofthe command.

The command packet length field 294 is the total number of bytes in thecommand packet header and the command payload. The destinationsubscriber unit ID field 296 is the MAC address of the destinationsubscriber unit or, for packets intended for all subscriber units, aspecial SUID for broadcast.

Command field 298 indicates the command type and provides any applicableparameters that the subscriber unit may need to effect and/or respond tothe command. If there is insufficient room in the command field, thisinformation may also be included as part of the payload, which carriesany data accompanying the command.

Command packets may be used, for example, to download firmware to thesubscriber units. From time to time, the access point broadcasts programupdates to the subscriber units through a series of command packets. Thecommand field in each packet identifies (1) the packet as being part ofa firmware update, (2) the update version number, (3) the subscriberunit hardware to which the firmware is applicable, and (4) a uniqueidentifier indicating the position of the payload's programming segmentin the overall program. If the currently running firmware version numbermatches the packet's version number, or if it doesn't have the sameapplicable hardware identified in the command, the subscriber unitignores the packet. If the subscriber unit satisfies these conditions,however, the subscriber unit accepts the packet and stores the programcode section carried by the command packet payload in a local buffer.

The access point inserts a checksum number in the last packet sentduring the update. When the subscriber unit receives this packet anddetects the checksum in the command field, the subscriber unit comparesthe checksum number to a checksum that it calculates using the bytesreceived in the update. If calculated and received checksums for the newfirmware match, the subscriber unit has correctly received the entirefirmware download, and it updates its flash memory to the newly receivedversion.

If the checksum does not match, the subscriber unit will continue toreceive the new packets from the AP and overwrite the same bufferlocations used previously. After the last packet is again received, thesubscriber unit again calculates the checksum and compares to thereceived checksum. Eventually, the checksums match, and the subscriberunit updates its firmware.

Referring now to FIGS. 19A and 19B, command packets, indicated at 304,sent from a subscriber unit to the access point are similar todownstream command packets from the access point. Like the access pointcommand packets, subscriber unit command packets include an RF preambleand header 306, a scrambled command packet header 308 and a scrambledpayload 310. Like the access point RF preamble and header, thesubscriber unit header 306 is added to the RF packet by the basebandprocessor.

Command packet header 308 includes a source subscriber unitidentification field 310, a command packet length field 312, adestination access point identification field 314, a command field 316and a checksum field 318. Source ID field 310 contains the originatingsubscriber unit's SUID. Command packet length field 312 includes thenumber of bytes in header 308 and payload 310. Command field 316indicates the type of command and may include responsive data.

Subscriber units primarily transmit command packets responsively tocommand packets received from the access point. In response to a rangingrequest, for example, the subscriber unit returns a command packet inwhich the command field identifies the packet as a ranging requestresponse and that includes the time stamp that was included in therequest packet. Under certain off-normal circumstances such as an alarmcondition that might indicate a failure, the subscriber unit mayoriginate a command packet that is not responsive to an access pointcommand. For example, the subscriber unit may perform self-diagnosticsand generate command packets to report the results of such analysis. Inthis event, the subscriber unit creates the command packet and storesthe packet in memory until receiving a transmit grant from the accesspoint.

Command packet payload 310 may include data related to the command. Thepayload may include for example, diagnostic information or an echo oftest bits sent by an access point command packet.

An upstream RF data packet 320 is similar to downstream RF data packet66 (FIG. 18). It includes an RF preamble and header 322, a scrambled MACdata packet header 324 and a scrambled MAC payload 326. The MAC datapacket header includes a source subscriber unit ID 328, a MAC datapacket length field 330, a destination access point ID 332 and a headerchecksum 334. Source subscriber unit ID field 328 includes thesubscriber unit's SUID. MAC data packet length field 330 includes thenumber of bytes in the MAC data packet header and the payload.Destination access point ID field 332 includes the access point's SUID.

Like the downstream data packet, the upstream data packet may include upto four packets for different destinations. Each payload section336A-336D, if all four are used, holds a separate Ethernet data packet.Corresponding length fields 338A-338D define the number of bytes foreach respective payload segment. Thus, upon receiving the RF datapacket, the access point reads the payload lengths, parses the payloadaccordingly, and outputs the parsed Ethernet data packets through itsEthernet port.

E. Antenna

Returning to FIGS. 3, 5 and 8, each access point and each subscriberunit includes a pair of antennas that are horizontally and verticallypolarized, respectively. It should be understood that any suitableantenna arrangement may be used. For example, a stackedelectromagnetically-coupled patch array antenna may include a pair ofprinted circuit board substrates stacked one above the other. Each boardhas a metal foil layer into which a plurality of patch elements areetched. The boards are not electrically connected and are separated byfoam or air. Stacked patch arrays should be understood in this art andare described in Kai Fong Lee and Wei Chen, Advances in Microstrip andPrinted Antennas 53-63 (1997). Stacked patch arrays may be used todefine a relatively large achievable bandwidth, for example 12%, but arerelatively expensive to produce.

Referring to FIG. 20, a patch array antenna 40 according to anembodiment of the present invention has a printed circuit board base 342upon which are disposed four rows of four patch elements 344 separatedfrom each other in each of the vertical and horizontal directions by adistance S. In the embodiment illustrated in FIG. 20, each patch is madefrom a stamped metal such as copper, brass or other high-conductivitymetal. The patch is a 0.898″ by 0.898″ square and is 0.015″ thick. Eachpatch sits 0.1″ above base 522, and distance S is 1.2″.

Base 342 is made of a R4003 substrate with two foil copper layers oneither side. In the present embodiment, the base is 0.035″ thick, but itmaybe made to any suitable thickness. The substrate is 0.032″ thick, andeach foil layer is 0.0015″ thick. The foil layers are etched to providepoints of attachment for the patch elements on one side and to provide afeed network on the other.

Each patch element has two connections to base 342. A center post 346 isstamped from the center of each patch element 344 and is soldereddirectly to upper copper foil surface 356. As is described in moredetail below, copper foil surface 356 is a ground plane. Since eachpatch element resonates primarily at its edges, however, there isminimal electrical current flowing at the direct connection between thecenter posts and the ground plane.

A feed post 350 is stamped from the edge of each patch element. Incontrast to the center post, feed post 350 extends from a lowerimpedance high-resonance area of the patch element, which conductselectric signals that correspond to the electromagnetic signals detectedby the patch element. To avoid grounding this signal, a relief area 352is etched into ground plane foil layer 356 to receive each feed post350. A relief area 354 is also defined in the ground plane for receiptof a coaxial connector, as described below.

Feed post 350 may be connected by a via, a conductive pin or other meansto a network of feed lines defined on an opposite side 348 of base 342.The feed lines are formed from a copper foil layer etched into acorporate feed network arrangement.

Procedures for etching patterns into a foil layer on a printed circuitboard should be well understood in this art. Generally, however, an etchresistant material is disposed on each side of base 342 over the areasat which it is desired for the copper foil to remain. Thus, the etchresistant material covers the entire side 356, except for relief areas352 and 354. On side 348, the etch resistant material is disposed overthe desired feed network. An etching agent is then applied to the foilsurfaces that removes all unmasked copper foil areas.

Before or after etching, holes are drilled through base 342 at eachrelief area 352 and 354, and 359. The edges of base 342 and surfaces 348and 356, except for the drilled holes, are covered, and the base isplaced in a suitable bath to prepare the cylindrical surfaces of thedrilled holes to receive a copper solution. Upon application of thecopper, the vias provide an electrical connection for the coaxialconnector and conductive paths from feed posts 350 to the feed networkdefined on side 348 that are isolated from the ground plane on side 348.Solder paste is then applied to vias inside the relief areas 352, andpatch elements 344 are placed on base 342 so that posts 350 are receivedby the vias inside the relief areas. Heat is applied so that a reflowseats posts 350 in the relief areas in electrical connection to thevias. Holes may also be drilled through the ground plane and the circuitboard to receive center posts 346 so that they may be set into positionfor soldering to the ground plane.

It should be understood that various methods may be employed forattaching the patch elements to the base and for electrically connectingthe elements to the feed network. For example, a pin may be insertedthrough base 342 to electrically connect a post 350 to the feed network.Thus, it should be understood that the structure described herein isprovided for purposes of example only.

A coaxial connector 358 has a center conductor 360 that extends into thevia at relief area 354 so that the center conductor is connected to thefeed network at 360 (FIG. 21). Four pins 359 extend through base 342 andthe ground plane and attach to the coaxial connector's outer conductor,thereby securing the coaxial connector in position and grounding theouter conductor.

Referring also to FIG. 21, the feed network is a “corporate” networkthat combines the power received from each patch element and deliversthe combined signal to center conductor 360 of coaxial connector 358. Inthe presently described embodiment, connector 358 is a 50 ohm connector,and each feed point 362 sees a 50 ohm impedance from its patch elementand via. At 5.77 GHz, a microstrip section 364 is a one-quarter wave 70ohm transformer between the 50 ohm impedance at 362 and a 100 ohmmicrostrip 366. Microstrip 366 combines in parallel with the 100 ohmmicrostrip from the neighboring patch element into a transformer 368.One-quarter wave 70.7 ohm transformer 368 transforms the resulting 50ohm connection to a 100 ohm microstrip 370. Microstrip 370 also combinesin parallel to a neighboring 100 ohm microstrip into a 70 ohmtransformer 372 to a 100 ohm microstrip 374. Microstrip 374, in turn,combines in parallel with a neighboring microstrip to a 70 ohmtransformer 376 into a 100 ohm microstrip 378. 100 ohm microstrip 378combines in parallel with a neighboring 100 ohm microstrip at a 50 ohmmicrostrip trace 380 that conveys the summed power to coaxial connector358 at 360.

Accordingly, the coaxial connector and the corporate feed network definea stable 50 ohm impedance network up to the patch elements. To operateat greatest efficiency, therefore, the patch elements should alsopresent an approximately 50 ohm impedance. As should be well understood,the patch elements themselves operate over a “radiation bandwidth” atwhich the array has a gain within a desired range, for example 17 dB±1dB. In the present embodiment described herein, the radiation bandwidthis between 5.725 GHz and 5.850 GHz. The patch elements' impedance,however, varies with frequency, and the elements only define animpedance giving an acceptable impedance match, or reflectioncoefficient, over a relatively small percentage of the radiationbandwidth. This percentage defines the antenna array's achievablebandwidth. Thus, for example, an antenna array with a radiationbandwidth centered at 5.77 GHz and having a 1% achievable bandwidth hasan operative frequency range of 5.77 GHz±0.029 GHz, i.e. 0.058 GHz overthe center frequency.

Of course, the range of what is considered an acceptable reflectioncoefficient may depend on the performance required of an antenna in agiven system. Reflection coefficient is a measure of how much energy isreflected back from the load compared to how much is transferred to theload. A voltage standing wave ratio (VSWR) within a range of 1.5 to 1.0may be considered good, although a VSWR of 2.0 to 1.0 may be acceptable.A 1.5 VSWR corresponds to a 0.20 reflection coefficient. A 2.0 VSWRcorresponds to a 0.343 reflection coefficient and a 0.5 dB mismatchloss, meaning that 0.5 dB of the achievable gain will be lost.

As should be well understood in this art, several things affect a patcharray's achievable bandwidth. Chief among these are dielectric thicknessand dielectric losses between the patch element and ground. In thearrangement illustrated in FIGS. 20 and 21, air is the dielectricbetween patch elements 344 and ground plane 356, thereby providingimproved gain and less loss over a non-air dielectric. Furthermore,because top surface 356 of base 342 defines the ground plane, theentirety of rear side 348 is available to define the feed network.Accordingly, the antenna arrangement allows a large degree of freedom indefining the network's physical structure to achieve a desired impedancematch.

The embodiment described herein defines an achievable bandwidth ofapproximately 2.5% for a VSWR of 1.5:1. It should be understood,however, that the various antenna parameters, for example the height ofthe elements above the ground plane and the spacing S between theelements, can be varied as desired to trade off gain, bandwidth andradiation sidelobe levels against each other. Additionally, because airmay not couple the patch elements to the ground plane as well as anon-air dielectric, the ability to minimize patch element spacing S maybe limited, depending on the construction of the patch elements, by theelements' tendency to couple with each other.

Furthermore, it should be understood that the antenna may otherwisevary. For example, the patch elements may define shapes other thansquares and may not necessarily be coplanar with each other. Inaddition, feed posts from multiple patch elements may connect to thesame feed point in a network that defines a suitable impedance match. Inaddition, the patch elements may be stamped and mounted to the printedcircuit board using surface mount techniques to reduce manufacturingtime.

As described above, each subscriber unit includes two patch arrays suchas shown in FIGS. 20 and 21. The array shown in FIG. 20 is verticallypolarized. The second patch array at the subscriber unit is identical tothe array shown in FIG. 20, except that it is rotated 90 degrees toestablish a horizontal polarization. In a preferred embodiment, theantenna arrays are disposed on the same printed circuit board, stackedone above the other. To improve the antenna's front to back ratio, whichmay be reduced due to feed line coupling, the edges of the feed side 348are grounded to the edge of a metallic enclosure that houses the antennaand the subscriber unit or access point.

The coaxial connector from each antenna array is connected to thesubscriber unit circuitry. The subscriber unit microprocessor controlsan electronic switch that selects the connection of one of the twoconnectors to the subscriber unit's transceiver.

Each access point also has a pair of oppositely polarized antenna arraysdisposed on a printed circuit board. The circuit board and patchelements are similar to the board and elements of the subscriber unitantenna. FIG. 22 illustrates the back surface of the access pointantenna circuit board base 380. Unlike the four-by-four subscriber unitarrays, the access point employs two eight-by-one arrays 382 and 384 forthe two polarizations to allow an asymmetric beam of 60 degrees by 10degrees. The two single-line arrays are disposed in parallel to eachother on the same circuit board base. The patch elements are disposed 90degrees with respect to each other. The vertically polarized array 44traverses the feed line 382 of the horizontally polarized array by asurface mounted capacitor or jumper 384 that is electrically isolatedfrom feed line 382.

Each subscriber unit includes in its memory a table that lists each ofthe six possible frequency channels at which an access point mightbroadcast. When the subscriber unit is first activated in the sector ofan access point, the subscriber unit microprocessor sequentially setsthe transceiver to each of the channels listed in the table. At each ofthe channel settings, the microprocessor controls the electronic switchbetween the coaxial connectors from the two arrays so that thesubscriber unit receives signals from one antenna polarization for afirst period of time and receives signals from the oppositely polarizedantenna array for the remaining time at which the transceiver is set tothe frequency channel. The microprocessor keeps the subscriber unit inreceive mode at each channel/polarization setting for a period of timerelated to a time in which it can be expected to receive a transmitgrant from the access point or recognize the access point expected toeventually send a transmit grant. Since the subscriber unit is, at thispoint, in group eight of the polling algorithm described above withrespect to FIG. 9, the timer at each setting should account for thetimer limits for that group.

If the subscriber unit fails to receive a transmit grant during thisperiod, it moves to the next channel/polarization setting and cyclesthrough these settings until receiving a transmit grant. Upon receivingthe grant, the subscriber unit thereafter remains at the setting atwhich the transmit grant was received. The subscriber unit remains atthe setting until re-started or until a system operator manually changesthe setting through a command packet transmitted from the access point.

FIGS. 23-25 illustrate an example of a stackedelectromagnetically-coupled patch array antenna. The antenna includes amain printed circuit board 850 and a secondary board 852 disposed inparallel to and above main board 850. The main board is 0.032″ thick andis made from ROGERS R4003 low loss material. Vertical-polarization andhorizontal-polarization main patch arrays 854 and 856 each comprisessixteen 0.473″ by 0.597″ patch elements 858 connected through acorporate feed network 860 to a connection point 862. The patch elementsand feed networks are etched, in a similar manner as discussed above,from a copper foil layer disposed on the top side 864 of main board 850.

A via extends through main board 850 at each connection point 862 fromtop side 864 to a bottom side (not shown) of the main board. A copperfoil layer (not shown) on the bottom side forms a ground plane. Reliefareas (not shown) are formed in the copper ground plane layer around theconnection point vias and partially around each of four holes 866disposed about the connection points. Vias may also be provided in holes866. At each connection point, a coaxial connector, like the connectordiscussed above with respect to FIG. 20, is attached from the bottomside of the main board so that a center conductor extends through thevia to electrically connect to the respective feed network. Pinsreceived in holes 866 ground the connector's outer conductor.

Vertical-polarization and horizontal-polarization parasitic patch arrays870 and 872 are disposed on a bottom side 874 of secondary board 852 sothat arrays 870 and 872 face main arrays 854 and 856 across anair-filled gap. In the present embodiment, the parasitic array sits0.170″ above the main array. Parasitic patch elements 876 are 0.473″ by0.793″ in size and are etched from a copper foil layer disposed onbottom side 874 in a similar manner as discussed above. The alignment ofthe parasitic array patch elements with respect to the main array patchelements is illustrated in FIG. 23, which overlays the parasitic arraysover the main arrays. As should be understood in this art, there is nofeed network on the secondary board, and there is no foil ground planeon the secondary board's top side (not shown). Secondary board 852 is0.008″ thick and is made from FR4 material. The secondary and mainboards may be separated from each other by non-conductive spacersextending between holes 878 in the main and secondary boards thatreceive the spacers. Alternatively, or additionally, the boards may besecured in an frame made from an ABS material.

FIGS. 23-25 illustrate a subscriber unit antenna arrangement. FIG. 26illustrates an overlay view of an access point antenna arrangement thatis very similar in structure to the subscriber unit antenna. The mainarrays are formed on the top side of the main board, and the parasiticarrays are formed on the bottom side of the secondary board. The mainand secondary boards are constructed in the same manner as the boards inthe subscriber unit antenna. Like the subscriber unit antenna, theaccess point main arrays output to feed networks etched on the mainboard's top side, whereas the secondary board has no feed networks orground plane. A ground plane foil layer is formed on the bottom of themain board, and a pair of coaxial connectors connect to the main boardbottom side, similarly to the connectors attached to the subscriber unitantenna. Three dark bands on either side of the main arrays representground areas left on the main board top surface. These areas do notaffect antenna performance and may be omitted. In one embodiment,RF-absorbent material is applied to the main board at these areas toreduce side lobes.

In the access point antenna, however, the vertical-polarization andhorizontal-polarization patch arrays are disposed in parallel singlelines. As with the subscriber unit array, parasitic patch elements 880are disposed 0.170″ above main patch elements 890 across an air gap.

Because of its wider achievable bandwidth (e.g. 12%), theelectromagnetically-coupled patch array antenna may be used in anembodiment in which the access point and the subscriber units maycommunicate over either of two frequency bands, as opposed to a singleband, using the same antenna. Using the antennas illustrated in FIGS.23-26, for example, the access point and subscriber unittransmitter/receivers may be configured to communicate at a 5.25-5.35GHz band, as well as the 5.725-5.850 GHz band discussed above.

The transmitter/receivers of the access point and the subscriber unitsare modified to allow switching between the different bands. Forexample, the subscriber unit transmitter/receiver, as shown in thefunctional diagram provided in FIG. 8, may be modified to include awideband VCO/PLL for a local oscillator that tunes from 4.77-5.37 GHz.The single RF transmit path (i.e. the upper path directed from left toright in FIG. 8) is replaced by two parallel paths, one using 5.8 GHzfilters and the other using 5.3 GHz filters. Two SPST switches areprovided to allow switching between the two paths, and digital circuitryis provided to control the switches. On the receiver path, a wider bandfilter is provided to cover both bands. Similarly, the power amplifieris replaced with a wideband RF power amplifier. Similar modificationsare made to the access point transmitter/receiver. Such modificationsshould be within the understanding of this art, and a more detaileddiscussion is, therefore, not provided herein. Moreover, it should beapparent that many variations in the transmitter and receiver circuitrymay be practiced.

While one or more preferred embodiments of the invention have beendescribed above, it should be understood that any and all equivalentrealizations of the present invention are included within the scope andspirit thereof. The embodiments depicted are presented by way of exampleonly and are not intended as limitations upon the present invention.Thus, it should be understood by those of ordinary skill in this artthat the present invention is not limited to these embodiments sincemodifications can be made. Therefore, it is contemplated that any andall such embodiments are included in the present invention as may fallwithin the literal or equivalent scope of the appended claims.

1. A patch array antenna, said antenna comprising: a planar base onwhich is defined a ground plane and feed positions that are electricallyisolated from the ground plane; a plurality of patch elements configuredto resonate over a predetermined frequency range, each patch elementisolated from the ground plane and disposed on the base over the groundplane so that an air dielectric is defined between the patch element andthe ground plane, and defining a resonant portion; a feed networkdefined on the base so that the air dielectric is between the patchelements and the feed network, wherein the feed network electricallyconnects the feed positions to one or more output points on the base;and with respect to each patch element, a respective metallic connectorelectrically connecting the resonant portion of the patch element and arespective said feed position.
 2. The antenna as in claim 1, wherein theground plane is defined on a first planar side of the base, and the feednetwork is defined on a second planar side of the base opposite thefirst side.
 3. The antenna as in claim 2, wherein the base is comprisedof a polymer substrate, wherein the ground plane is comprised of ametallic foil sheet on one side of the polymer substrate, and the feednetwork is comprised of metallic foil traces on an opposite side of thepolymer substrate.
 4. The antenna as in claim 3, wherein the feednetwork is a corporate network extending from the feed positions to asingle output point.
 5. The antenna as in claim 1, wherein each patchelement includes a planar metallic main portion.
 6. The antenna as inclaim 5, wherein the main portions are disposed in a common plane. 7.The antenna as in claim 6, wherein each patch element forms therespective metallic connector, and wherein the metallic connectorextends from a resonant area of the main portion to the base and iselectrically connected to a respective feed position.
 8. The antenna asin claim 7, wherein each patch element includes a post extending from anon-resonant area of the main portion to the base.
 9. The antenna as inclaim 7, wherein the patch elements are disposed so that the mainportions and metallic connectors of the patch elements are in the samealignment and define an antenna polarization.
 10. A patch array antenna,said antenna comprising: a planar base having a substrate, on a firstplanar side of which is defined a metallic foil ground plane and feedpositions that are electrically isolated from the ground plane andextend through the substrate to an opposite second side of thesubstrate; a plurality of patch elements configured to resonate over apredetermined frequency range, each patch element isolated from theground plane and disposed on the base over the ground plane so that anair dielectric is defined between the patch element and the groundplane, including a planar metallic main portion defining a resonant areaand disposed in a common plane with the main portions of the other patchelements, and including a metallic first post extending from theresonant area to the base and electrically connecting the resonant areato a respective feed position, wherein the patch elements are disposedso that the main portions and first posts of the patch elements are inthe same alignment and define an antenna polarization; and a metallicfoil trace feed network defined on the second side of the substrate thatelectrically connects the feed positions to one or more output points onthe base.
 11. The antenna as in claim 10, wherein each patch elementincludes a second post extending from a non-resonant area of the mainportion to the base.
 12. The antenna as in claim 10, wherein the mainportions are square shaped.
 13. The antenna as in claim 11, wherein thefirst and second posts are stamped from the main portion.
 14. A point tomultipoint wireless communication system, said system comprising: anaccess point configured to receive data signals from an external system,the access point having an antenna, a processor, and circuitry incommunication with the access point antenna and controlled by the accesspoint processor to transmit wireless electromagnetic signalscorresponding to the data signals to, and to receive wirelesselectromagnetic signals from, a geographic area; and a plurality ofsubscriber units disposed within the area, each said subscriber unithaving an antenna, a processor and circuitry controlled by thesubscriber unit processor to transmit wireless electromagnetic signalsto, and receive wireless electromagnetic signals from, the access pointfor communication with the external system, wherein each of the accesspoint antenna and the subscriber unit antennas includes a planar base onwhich is defined a ground plane and feed positions that are electricallyisolated from the ground plane, a plurality of patch elements configuredto resonate over a predetermined frequency range, each patch elementisolated from the ground plane and disposed on the base over the groundplane so that an air dielectric is defined between the patch element andthe ground plane, and defining a resonant portion, a feed networkdefined on the base so that the air dielectric is between the patchelements and the feed network, wherein the feed network electricallyconnects the feed positions to one or more output points on the base;and with respect to each patch element, a respective metallic connectorelectrically connecting the resonant portion of the patch element and arespective said feed position.
 15. The system as in claim 14, whereinthe ground plane is defined on a first planar side of the base, and thefeed network is defined on a second planar side of the base opposite thefirst side.
 16. The system as in claim 15, wherein the base is comprisedof a polymer substrate, wherein the ground plane is comprised of ametallic foil sheet on one side of the polymer substrate, and the feednetwork is comprised of metallic foil traces on an opposite side of thepolymer substrate.
 17. The system as in claim 14, wherein each patchelement includes a planar metallic main portion, the main portions aredisposed in a common plane, and each patch element forms the respectivea metallic connector, and wherein the metallic connector extends from aresonant area of the main portion to the base and is electricallyconnected to a respective feed position.
 18. The system as in claim 17,wherein each patch element includes a post extending from a non-resonantarea of the main portion to the base.
 19. The system as in claim 17,wherein the patch elements are disposed so that the main portions andmetallic connectors of the patch elements are in the same alignment anddefine an antenna polarization.
 20. The system as in claim 19, whereineach of the access point and the subscriber units includes a first saidantenna and a second said antenna respectively aligned in vertical andhorizontal polarization.
 21. The system as in claim 20, wherein thecircuitry of each of the access point and the subscriber units isconfigured to selectively switch between the first antenna and thesecond antenna.
 22. A point to multipoint wireless communication system,said system comprising: an access point configured to receive datasignals from an external system, the access point having an antenna, aprocessor, and circuitry in communication with the access point antennaand controlled by the access point processor to transmit wirelesselectromagnetic signals corresponding to the data signals to, and toreceive wireless electromagnetic signals from, a geographic area; and aplurality of subscriber units disposed within the area, each saidsubscriber unit having an antenna, a processor and circuitry controlledby the subscriber unit processor to transmit wireless electromagneticsignals to, and receive wireless electromagnetic signals from, theaccess point for communication with the external system, wherein each ofthe access point antenna and the subscriber unit antennas includes aplanar base having a substrate, on a first planar side of which isdefined a metallic foil ground plane and feed positions that areelectrically isolated from the ground plane and extend through thesubstrate to an opposite second side of the substrate, a plurality ofpatch elements configured to resonate over a predetermined frequencyrange, each patch element isolated from the ground plane and disposedover the ground plane so that an air dielectric is defined between thepatch element and the ground plane, including a planar metallic mainportion defining a resonant area and disposed in a common plane with themain portions of the other patch elements, and including a metallicfirst post extending from the resonant area to the base and electricallyconnecting the resonant area to a respective feed position, wherein thepatch elements are disposed so that the main portions and first posts ofthe patch elements are in the same alignment and define an antennapolarization, and a metallic foil trace feed network defined on thesecond side of the substrate that electrically connects the feedpositions to one or more output points on the base.
 23. The system as inclaim 22, wherein each patch element includes a second post extendingfrom a non-resonant area of the main portion to the base.
 24. A patcharray antenna, said antenna comprising: a planar base on which isdefined a ground plane and feed positions that are electrically isolatedfrom the ground plane; a plurality of patch elements configured toresonate over a predetermined frequency range, each patch elementisolated from the ground plane and disposed on the base over the groundplane so that an air dielectric is defined between the patch element andthe ground plane, and defining a resonant portion; a feed networkdefined on the base so that the air dielectric is between the patchelements and the feed network; and with respect to each patch element, arespective metallic connector electrically connecting the resonantportion of the patch element and a respective said feed position,wherein the feed network electrically connects the feed positions to oneor more output points on the base, the ground plane is defined on afirst planar side of the base, the feed network is defined on a secondplanar side of the base opposite the first side, and the first side ofthe base is between the patch elements and the second side of the base.25. The antenna as in claim 24, wherein the base is comprised of apolymer substrate, wherein the ground plane is comprised of a metallicfoil sheet on one side of the polymer substrate, and the feed network iscomprised of metallic foil traces on an opposite side of the polymersubstrate.
 26. The antenna as in claim 24, wherein the feed network is acorporate network extending from the feed positions to a single outputpoint.